Conventionally, centrifugal pumps and roller pumps have been mainly used as assist pumps for extracorporeal circulation during and after cardiac operation (hereinafter “a blood pump”) and as an advance preparation (bridge-to-decision) prior to an implant of long term artificial heart. (Refer to the patent literature 1, for example). There has been little necessity for saving weight of the blood pump itself because blood pumps are ordinarily operated by being placed at the side of a surgical table in an operation room or at the side of the bed in medical wards along with drive means such as drive motors in many cases.
Also, centrifugal pumps are accepted as being economical within a certain scope though they have some cost due to the usage of disposable pump heads, and they have the merit of high pressure generation even for a high flow situation. However, centrifugal pumps have problems when they are operated as portable blood pumps because the centrifugal pumps contain motor drive units that are not disposable and weigh more than 1 Kg (1.6 Kg for example).
On the other hand, roller pumps have an advantage of being economical because patient consumables are only tubes. However, it is difficult for roller pumps to be operated continuously for a long term such as more than a week due to fatigue breakdown of tubes.
Recently, durability of mechanical circulatory support pumps has been improved and the demand for artificial hearts has become intense and consequently usage of blood pumps mentioned above has increased and blood pumps which are low cost, compact, lightweight and portable are required.
Also, a configuration to place a stator at the periphery of a centrifugal pump has been conventionally known in a centrifugal pump used for a blood pump. However, there is a problem in that such a configuration makes a centrifugal pump itself larger in the diametrical direction and consequently the equipment becomes larger.
Under such circumstances, inventors have already proposed a magnetic levitation pump with small sized dynamic pressure bearings (refer to patent literature 2) in which a stator and a rotor are disposed along the axis direction and the rotor is rotatable with a magnetic levitation status. The proposed magnetic levitation pump with small size dynamic pressure bearings is equipped with an axial-flow impeller and dynamic pressure bearings, and is also equipped with a rotation axis body having permanent magnets at each end and a magnetic coupling means disposed in such a manner that said magnetic coupling means faces each end of the rotation axis body.
However, in the proposed magnetic levitation pump with dynamic pressure bearings, the magnetic coupling means was closely integrated to the pump main body and the magnetic coupling means was not easily dismounted from the pump main body. After the proposed magnetic levitation pump is used as an auxiliary pump for internal circulation, it is currently difficult to use the magnetic levitation pump for other operations or other patients, from a hygiene perspective and also a perspective of blood clot formation, and the situation is that the magnetic levitation pump is disposed of after it has been used once.
Also, an implantable axial-flow blood pump containing a blood immersed axle bearing is known as one type of axial-flow pump. (Refer to the patent literature 3) In the configuration of the axial-flow blood pump disclosed in the patent literature 3, a cup 34 equipped with a stator impeller 30 and a cup 54 equipped with an exit stator impeller 48 are attached to anterior and posterior balls (38, 52) of a pump rotor 20 that is housed in a housing 12. The stator impeller 30 and the exit stator impeller 48 fit the inner periphery of the housing 12 to function as a bearing for the pump rotor 20. The pump rotor is equipped with a rotor blade 44 that accelerates blood flow and the blood flow velocity is lowered by an exit stator blade 48 and the rotation is stopped to drain the blood toward the exit 18. Note that the motor stator 22 is secured in such a manner that the motor stator 22 encircles the periphery of the stator tube 23 that is secured on the inside of the housing 12. (Refer to FIGS. 1 to 4; paragraphs 0013 to 0016 of the patent literature 3)
As has been mentioned above, it is observed in the configuration of the axial-flow blood pump disclosed in the patent literature 3 that the structure of the housing 12 is complicated and de-installation of the motor stator 22 is accordingly difficult.
Currently, the technology of implantable auxiliary artificial hearts made of Titanium is well established. However, many patients exist to whom auxiliary artificial hearts cannot be applied. Those patients are children with antithrombogenicity at a low blood flow rate and also elderly people whose heart transplant registration is not permitted. Children require blood pumps that are extremely compact and lightweight, with antithrombogenicity at a low blood flow, and for these reasons the pump has to be selected not from transplantable types but from extracorporeal types and consequently axial-flow pumps that can adopt long and thin motor magnets and can be made small are befitted. Also for elderly people, auxiliary artificial hearts must be made of polymer materials, not of metals, and must have a structure that realizes a pump with a reusable driving portion, in consideration of the cost.